This invention relates to a method and apparatus for correcting a machine tool in general and, in particular, to a new and useful method and device for correcting tool lengths and tool radii particularly for numerically controlled machines equipped with positional path measuring systems by means of nominal-actual value comparison.
While preparing part programs for numerically controlled machine tools, particularly work stations, the control of the tool length and tool radius during a milling operation, for example, starts from the nominal dimension of the tool or from the dimension equal to zero of the length or radius of the tool. The actual deviations from a nominal or zero dimension are entered into the numerical control separately as so-called tool length or tool radius corrections. This is usually done by hand or by means of a special punched tape.
In order to determine the respective actual dimension, the length and, if needed, also the cutting radius of each tool, each individual tool must be measured prior to starting the job. With large tool sets, a long total time is spent for this purpose. Also, measuring the correction values and transferring them, for example, to punched tapes, or entering such values into a numerical control, normally involves risks of error. These are errors which, under the most favorable conditions lead to rejects, and under the most unfavorable conditions, can cause considerable damage or even destruction of the tool. Automatic measuring of the tools and thus determining as well as entering of the corrections into the numerical control eliminates these errors and minimizes the time needed therefor.
Designs are known in which this problem is solved by providing additional measuring systems as a permanent part of the equipment of the machine. However, this means that one or more measuring systems for automatically determining the tool length and radius corrections are necessary in addition to the measuring systems (X-Y- and Z-axis) which are also needed in a numerically controlled machine. These costs are very high and unfavorably affect the economy of such equipment.